|Index||-||FAQ - Cart Help Buttons - Cart Settings - 5. Tax Settings|
Tax ID values can be created for your tax exempt customers. Any customer who enters a valid Tax ID into the shopping cart will not be charged tax on their purchase.
Simply create your own numbers and enter them into the cart admin, then give them to your tax exempt merchants.
They will then be able to enter them into the shopping cart to exempt the order from being taxed.